Purpose:
The aim of this study was to determine the temporal pattern of central macular thickness (CMT) improvement after epiretinal membrane peel surgeries performed at a teaching institution (Massachusetts Eye and Ear Infirmary).

Methods:
This is a retrospective review of 23 patients who underwent vitrectomy and membrane peel for idiopathic epiretinal membrane (ERM) between 2010-2012 at the Massachusetts Eye and Ear Infirmary. Visual acuity and spectral-domain optical coherence tomography (SD-OCT) images were analyzed to compare pre-operative values from post-operative day one (POD1), and week one (POW1), and months 1-3 (POM1-3).

Results:
Of the 23 patients reviewed, 16 had pars plana vitrectomy (PPV) with membrane peel (MP) alone and 7 had PPV/MP with phacoemulsification of their cataract at the same time. Pre-operatively, the average visual acuity (VA) was 0.65 log minimal angle of resolution (logMAR) (standard deviation ± 0.30) and the average OCT central macular thickness (CMT) was 476 μm ± 90. The average visual acuity at POD1, POW1, and POM1-3 was 1.00 logMAR ± 0.45, 0.77 logMAR ± 0.53, and 0.49 logMAR ± 0.29, respectively, demonstrating that while visual acuity initially worsened in the immediate post-operative period, it eventually improved during the POM1-3 time frame. Ultimately, 73.9% of patients enjoyed an improvement in visual acuity, with an average improvement of -0.17 logMAR (P=0.02). The average CMT at POD 1, POW1, and POM1-3 was 428 μm ± 98, 399 μm ± 106, and 349 μm ± 83, respectively. This represents a 25.1% (P=0.004), 35.2% (P=0.002), and 53.9% (P<0.001) reduction in CMT at POD1, POW1, and POM1-3, respectively, as compared to pre-operative values. The top five responders at POW1, who had an average 70% reduction in CMT, ultimately had an average improvement in VA of -0.48 logMAR, which is markedly better than the overall average. Conversely, the bottom five responders at POW1 had an average 5% increase in CMT, which were associated with an overall average -0.17 logMAR reduction in VA.

Conclusions:
Our study shows that 50% of the anatomical improvement after ERM peel surgery is seen in the first day/week after the surgery. Improvement of macular thickness precedes the VA improvement and the improvement seen in the first week can be used to help predict the final visual acuity.